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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


1967 Triumph Bonneville Carburetor Issues

Motorcycle Classics tech expert Keith Fellenstein

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Carburetor issues

Q: I have a 1967 Triumph Bonneville with 18,000 miles on it. It recently started running with a rough exhaust note once it was warm. After sitting all winter it started with one kick, but from then on it ran very rough. The left cylinder exhaust ran hot on start. The pipe and exhaust were hot while the right side was cool. I thought maybe I had a tight exhaust valve, so I adjusted it. It was better, but still not right, so I readjusted it, and the left cylinder went back to running hot. It still starts on the first kick. I have also noticed that the carburetor ticklers take forever to flow, where in the past they filled more quickly. – Peter/via email

A:  When you say the right pipe was cool it sounds like maybe the right cylinder wasn’t firing, or did you mean that in comparison to the left it was cooler? Assuming you meant the latter, and knowing that it sat all winter, I’d suspect a restricted/clogged jet on the left carburetor leading to a lean condition for that cylinder. Just to be sure of the state of the fuel system, I’d pull the carburetors and clean them both. Since you mention difficulty in getting the ticklers to work well, double check the float heights. They shouldn’t change on their own; they are difficult enough to change on purpose unless you are using the new StayUp floats. Another possibility if the bike is still on points would be timing differences, with the left cylinder running with the timing retarded in relation to the right cylinder, but since you said it ran well enough when parked I’d check the fuel delivery system first.